Electric power substations distribute three-phase power from sets of primary transmission lines to one or more sets of secondary lines, which in turn distribute the power to residential, commercial, and industrial loads. The primary transmission lines connect to the secondary lines at a power grid (a.k.a. bus) located within the substation.
Generally, each transmission line connected to the power grid is equipped with a power circuit breaker. These power circuit breakers protect the substation equipment and the entire transmission system from harmful fault currents caused by overloaded or short-circuited transmission lines. Various types of power circuit breakers exist, including air, oil or vacuum, but their operation is generally similar. Pairs of opposing contacts are normally closed to complete the transmission path through the circuit breaker. Sensors monitor the current flowing through the transmission path. These sensors send current level information to protective relay equipment which is centrally located within a control panel. The relay equipment determines whether a fault current exists and, if so, generates and sends a trip signal to the appropriate breaker control equipment also located on the control panel. The breaker control equipment in turn causes the circuit breaker to trip open. The circuit breaker trip operation forces the contacts apart by fluid or air pressure. The circuit breaker is reset by a close operation wherein the contacts are closed in the same manner.
The above-mentioned control panel may be located on the circuit breaker itself, or may be remotely located within a separate walled enclosure within the substation. Here an operator can view and manually control the operation of the circuit breakers.
Regular testing of the relay equipment and breaker control equipment is conducted. During such testing, the transmission line to which the circuit breaker is attached must be disconnected from the power grid while the circuit breaker and support equipment remain operational. An operator then performs a manual test procedure to verify the integrity of the relay equipment and breaker control equipment. The test procedure includes manual operation of the relay equipment and breaker control equipment from the control panel to ensure that the circuit breakers will trip and reclose.
In the past, this testing required tripping and reclosing the circuit breaker at least twelve times over the course of one test procedure. After two such operations the fluid pressure in the circuit breaker would need replenishment. Pressurization involved running a compressor for 30 minutes or more, all of which was time wasted by the operator.
Furthermore, two such test procedures were performed over the course of a year. The tripping and closing of the circuit breakers and charging by a compressor caused excessive wear and tear on this equipment.
In addition, a breaker failure function is built into the control panel to provide back-up relay and control equipment in case of failure of the primary equipment. In order to test the breaker failure function, the operator was required to manually disconnect the primary equipment from the control panel. This was done by unscrewing the terminal screws and unfastening the wires which connected the equipment inside the control panel. Such testing was unduly time consuming and complex, and created a risk of electric shock to the operator.
There have been no known previous efforts at solving the above-mentioned problems.